The Role And Mechanism Of The Hippocampal-Prefrontal Pathway In Sepsis-associated Encephalopathy In Mice

Aims: Sepsis-associated encephalopathy(SAE)often leads to cognitive and psychiatric deficits.However,the pathophysiology of SAE is complex and unclear.Hippocampus(HPC)-prefrontal cortex(PFC)pathway is a key signaling pathway mediating cognitive dysfunction.The role of HPC-PFC in SAE was not reported.Here,we aimed to investigate the role of HPC-PFC pathway in SAE.Methods: The experiment was divided into two segments.The first segment explored the role of the HPC-PFC pathway in cognitive dysfunction and anxiety-related behavior of CLP-induced sepsis.Firstly,we identified neural projections from the HPC to the PFC via a retrograde tracer(Fluoro-Gold)and anterograde neural tract tracing with adeno-associated virus(AAV).Secondly,cecal ligation and puncture(CLP)was used to induce an animal model of SAE.Then,we employed chemical genetics approaches to assess the effect of activation of the HPC-PFC pathway on cognitive function and anxiety-related behaviors in sepsis mice.Excitatory neurons were evaluated via immunofluorescent staining of c-Fos-positive neurons in PFC.Finally,Morris water maze(MWM),Barnes maze(BM),and new object recognition(NOR)were used to evaluate cognitive function.Elevated plus maze(EPM)and Open field test(OFT)were used to assess anxiety-related behavior.In the second segment,we further explored the potential mechanism involved.The methods of virus injection,cannula implantation,and modeling were described previously.Glutamate receptor antagonist or saline was injected bilaterally using the guide cannulas in m PFC 30 min prior to CNO injection.MWM and BM were used to assess spatial learning and memory in animals as described before.The expressions of m Cherry and c-fos in HPC and PFC were detected by immunofluorescence.Western Blot(WB)was used to detect the expression levels of calmodulin-dependent protein kinase(Ca MKIIa),cyclic adenosine phosphate reaction element-binding protein(CREB)or phosphorylated CREB(p CREB),and brain-derived neurotrophic factor(BDNF).Results: The neural projection from HPC to PFC has been successfully identified.Chemogenetic activation of the HPC-PFC pathway improved CLP-induced spatial memory but not cognitive memory and anxiety-related behaviors.The activation of the HPC-PFC pathway resulted in significantly increased levels of Ca MKIIa,p CREB,and BDNF in PFC.Glutamate receptor inhibitors(D-AP5 or NBQX)can block the role of HPC-PFC pathway in improving spatial memory in septic mice,and prevent the up-regulation of Ca MKII/CREB/BDNF signaling pathway.Conclusions: Activation of the HPC-PFC pathway can improve spatial memory impairment induced by CLP-induced sepsis in mice.Glutamate receptors and their downstream signaling Ca MKII/CREB/BDNF pathway may be an important molecular mechanism connecting the HPC-PFC pathway with cognitive dysfunction in SAE.There are 31 figures,5 tables and 209 references...